Controlled alteration of the shape and conformational stability of α-helical cell-lytic peptides: effect on mode of action and cell specificity

Abstract

A novel method, based on the rational and systematic modulation of macroscopic structural characteristics on a template originating from a large number of natural, cell-lytic, amphipathic alpha-helical peptides, was used to probe how the depths and shapes of hydrophobic and polar faces and the conformational stability affect antimicrobial activity and selectivity with respect to eukaryotic cells. A plausible mode of action explaining the peptides' behaviour in model membranes, bacteria and host cells is proposed. Cytotoxic activity, in general, correlated strongly with the hydrophobic sector depth, and required a majority of aliphatic residue side chains having more than two carbon atoms. It also correlated significantly with the size of polar sector residues, which determines the penetration depth of the peptide via the so-called snorkel effect. Both an oblique gradient of long to short aliphatic residues along the hydrophobic face and a stabilized helical structure increased activity against host cells but not against bacteria, as revealed by haemolysis, flow cytofluorimetric studies on lymphocytes and surface plasmon resonance studies with model phosphatidylcholine/cholesterol membranes. The mode of interaction changes radically for a peptide with a stable, preformed helical conformation compared with others that form a structure only on membrane binding. The close correlation between effects observed in biological and model systems suggests that the 'carpet model' correctly represents the type of peptides that are bacteria-selective, whereas the behaviour of those that lyse host cells is more complex.

Computational Design of Highly Selective Antimicrobial Peptides

“…On the basis of a statistical analysis of natural helical AMPs, 8 glycine residues have an increased frequency at position 7 or 14. It was shown that placing a Gly residue at position 7 in an artificial 19-residue helical AMP, 28 somewhat increased selectivity, while placing Gly in position 14, or both 7 and 14 considerably reduced antimicrobial potency; so there seem to be positional requirements for its use in increasing selectivity. Using the D-descriptor in connection with the AMP-Designer algorithm, it was possible to simultaneously introduce 6 internal glycine residues without markedly reducing activity toward Gram-negative microorganisms, while dramatically increasing selectivity.…”

Evaluation of Strategies for Improving Proteolytic Resistance of Antimicrobial Peptides by Using Variants of EFK17, an Internal Segment of LL-37

“…Furthermore, since the W substitutions may in our case have a reducing effect on peptide hydrophobicity depending on the hydrophobicity scale employed, it is of interest in the present context since it has been found that an increased level of hydrophobicity for helical amphiphilic AMP may specifically increase the lytic property on erythrocytes rather than bacteria (67). The lower hydrophobicity and increased penetrability of negative membranes both indicate that the W-modified variant would have a higher bactericidalto-cytotoxic ratio.…”

Easy Strategy To Protect Antimicrobial Peptides from Fast Degradation in Serum

“…Surprisingly, the distance of the positive charge of the antimicrobial peptides from the negatively charged lipid heads of the bacterial membrane seems not to play a role in the antibacterial activity. In a study using ␣-helical cell lytic peptides, the exchange of lysine against ornithine and 2,4-diaminobutyric acid (Dab), also had only a small effect on the MIC; however, faster kinetics was seen, due to the snorkel effect (6).…”